1. Field of the Invention
The present invention relates generally to communication systems and, more particularly, to wireless broadband communication networks and methods for data transmission and reception.
2. Related Art
There is an increasing demand for interconnecting a plurality of remote locations spread over a large geographic area to provide broadband data communication services to those locations. The objective of many of these types of systems is to transfer large amounts of data, voice, or video between the various remote locations and a central location, which provides a gateway to a larger network, such as, for example, the Internet. Alternatively, for example, many of these types of systems can be used for private networks where the end-to-end transfer of data takes place between any of the two remote locations.
Current solutions for such networks include both wired and wireless approaches. If a wired network does not already exist or is otherwise inadequate to provide the required broadband service, then a wireless approach has many advantages. In general, wireless solutions are easier and quicker to install and, therefore, are significantly less expensive.
As an example, one wireless network solution to the problem provides point-to-point wireless connectivity to all the remote locations. This approach requires many locations to be equipped with multiple transceivers, each one connected to a different directional antenna. At those sites, a router or multiplexer may also be required to provide switching capability between the several point-to-point links. This approach is both costly and under utilizes the radio frequency (RF) bandwidth. Data applications are characterized by sudden bursts of high-speed communications followed by long idle times. The point-to-point links therefore need to be designed to support the high data rate required for the burst, but will otherwise be idle at other times.
Another wireless access solution, for example, is based on a point-to-multipoint topology consisting of a central base station with the capability of handling communications with a plurality of subscriber stations. These point-to-multipoint systems use various medium access mechanisms to coordinate how the subscribers are all served by a single base station. These may include Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), and Code Division Multiple Access (CDMA). The base station, having direct access to all the subscribers, provides centralized control to perform bandwidth sharing and allocation between the subscribers.
The geographic coverage of a single point-to-multipoint system is limited by the range of the radio equipment and line-of-sight (LOS) limitations. When the required geographic coverage exceeds the RF range of the equipment, these systems require multiple neighboring base stations, each at the center of a xe2x80x9ccell.xe2x80x9d Within each cell, subscriber stations communicate with the base station that is nearest to them. The cells are ideally distributed on a honeycomb grid with the base stations at the center of each hexagon.
Deployment of cell-based systems generally encounter many difficulties. For example, traffic is concentrated at the various base stations, but still needs to be carried to a single central point through an additional backbone network. This backbone needs to be deployed with the maximum capacity envisioned, even though, at the early stages of deployment, it will be greatly underutilized. This represents an up-front expense before the service comes online.
Additionally, topographical features will shadow or block areas resulting in inadequate or a total loss of coverage. Studies have shown that in a cell-based system, up to thirty percent of potential subscribers may not be reached due to LOS limitations. This percentage can be reduced using mini-cells to cover some dark areas (i.e., uncovered areas); however, the additional base stations and the associated backbone connections add to the cost and complexity of the cell-based system.
A third wireless access solution, for example, is based on a multipoint-to-multipoint or mesh topology. In this approach, each station is equipped with an omnidirectional antenna and must be within RF reach of other stations in the network. The transceivers transmit to and receive from their direct neighbors and forward packets to their various destinations using any one of many possible routes. This approach does not require a backbone and can easily reach hidden locations through multiple hops.
The multipoint-to-multipoint approach, however, has many drawbacks. For example, to establish connectivity to more than one neighbor, the radio antenna will typically be an omnidirectional or sector antenna (as opposed to the directional antenna used by the subscriber stations in a point-to-multipoint system). This reduces the link distance that can be achieved between any two points and exposes the receiver to noise and interference from all directions.
Another drawback is that each radio station may have a large number of neighbors that can be reached with one hop. This is indeed the advantage of the mesh networkxe2x80x94provide multiple alternate routes between any two points. However, the transmissions from any given radio will reach not only the intended receiver, but also all of the neighboring receivers. Thus, the number of possible simultaneous transmissions by neighboring radios must be greatly reduced in order to avoid collisions.
An additional drawback is that, due to the possibility of collisions (as discussed above), all of the radio stations need to coordinate their transmission times with neighboring radio stations without the help of a central site. This must be done with over-the-air messages, which further reduces the airtime available for actual data transmissions.
As a result, there is a need for a wireless communication network system and method that overcomes some of the limitations of the prior art, such as, for example, those discussed for a cell-based point-to-multipoint system or for a mesh multipoint-to-multipoint topology.
In accordance with some embodiments of the present invention, scalable network topologies and access methods (e.g., medium access control) using frequency, time, and directional diversity are provided. Wireless broadband data access is provided to and from a plurality of locations distributed randomly over a large geographic area. Various network topologies and access methods are provided, which allow numerous transmitting instruments to co-exist without loss of the communication link or information (e.g., data packets) due to collisions or conflicts within the network or system.
Embodiments of the present invention may include, for example, an apparatus and method that facilitates the deployment of a RF wireless network having many advantageous characteristics. As an example, the network can be deployed one node at a time without requiring base stations. A new node can become part of an existing network by simply being placed within RF reach of any other node already in the network. In addition, once the new node is part of the network, the new node can become the attaching point for other new nodes.
Furthermore, in accordance with some embodiments of the present invention, network nodes only require two independent communication channels and may combine the use of frequency and directional diversity to allow multiple nodes to transmit simultaneously in the same geographical area without collisions. The network does not require a backbone to be deployed, with all traffic capable of being forwarded by the wireless apparatus, through multiple hops, if necessary, to reach its intended destination. Backbone point-to-point links can be added at a later time to scale-up the network, if desired, but are not needed until the total available capacity has been utilized. An additional advantage is that the apparatus deployed at each subscriber location, for example, may be identical for all locations (e.g., no hub or base station equipment is required). Furthermore, in accordance with some embodiments of the present invention, the medium-access method self-synchronizes all of the nodes in the network with no overhead or dedicated synchronization transmissions.
In accordance with one embodiment of the present invention, a wireless communications network is provided that includes a plurality of locations, each having a transceiver adapted to transmit or receive a radio frequency signal by selecting a channel from at least two non-conflicting channels and further adapted to connect to two distinct antennas. One of the locations is designated a root node and the other locations are designated as non-root nodes, with each non-root node within radio frequency range of either the root node or another non-root node. A tree structure is formed that originates at the root node and branches out from the root node to one or more of the non-root nodes, with the locations not within radio frequency range of the root node communicating with the root node through non-root nodes that function as repeaters. The repeaters are designated as parents and the non-root nodes that communicate with the repeaters are designated as children for each level of the tree structure. A broadbeam antenna is connected to the transceiver of the root and parent nodes to transmit or receive wireless communications with the non-root nodes that are within radio frequency range of the root or parent nodes. A directional antenna is connected to the transceivers of the non-root nodes to transmit or receive wireless communications with the root or parent node.
In accordance with another embodiment of the present invention, a method of communicating in a wireless communications network is provided, with the network comprised of a root node and at least one repeater node and one leaf node. The root node has an antenna for wireless communication with its slaves while the repeater nodes and the leaf nodes have only one master and have a directional antenna pointed at the respective master. The repeater nodes have an additional antenna for wireless communication with their slaves when functioning as masters. The method performed by each root, repeater, and leaf node comprises determining the node type; performing a master cycle repeatedly if the node is the root node; performing an attach cycle if unattached or becomes detached from the network and if the node is not the root; and performing a slave cycle followed by the master cycle, repeatedly, if the node is not the root.
A more complete understanding of embodiments of the present invention for network topology systems and methods will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly.